Merge pull request #24 from mbullington/revert-nullsafe

Revert null-safe change.
diff --git a/pubspec.yaml b/pubspec.yaml
index 3b9d027..3de0fc6 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,9 +1,8 @@
 name: node_preamble
 author: Michael Bullington <mikebullingtn@gmail.com>
 homepage: https://github.com/mbullington/node_preamble.dart
-version: 1.4.13-nullsafety
+version: 1.4.12
 description: Better node.js preamble for dart2js, use it in your build system.
 
 environment:
-  sdk: '>=2.12.0-0 <3.0.0'
-
+  sdk: '>=1.24.0 <3.0.0'